Flux dependence of carbon chemical erosion by deuterium ions

Abstract

The chemical erosion of carbon in interaction with a hydrogen plasma has been studied in detail in ion beam experiments, and erosion yield values are available as a function of ion energy and surface temperature. However, the conditions in the ITER divertor cannot be simulated by ion beam experiments, especially as far as ion flux is concerned.Therefore, a joint attempt was made through the EU Task Force on plasma-wall interaction and the international tokamak physics activity involving seven different fusion devices and plasma simulators to clarify the flux dependence. For each data point the local plasma conditions were normalized to an impact energy of 30 eV, care was taken to select data for a surface temperature close to the maximum yield or room temperature and the calibration of the diagnostic was performed in situ. Through this procedure the previous large scatter was significantly reduced, revealing a clear trend for a decreasing yield with increasing ion flux, . After the attribution of an error to each data point a fit using Bayesian probability analysis was performed, yielding a decrease in the erosion yield with −0.54 at high ion fluxes.

The impact of divertor detachment on carbon sources in JET L-mode discharges

“…Seeding impurities such as argon will be applied in addition to increase the radiative fraction. Chemical sputtering at these low T surface is caused by ion induced desorption of hydrocarbon radicals and not by thermal emission of hydrocarbon radicals enhanced by radiation damage as described in [3]. The later mechanism will dominate the chemical sputtering in ITER at the expected target temperatures.…”

“…The impact energy of fuel ions drops below the threshold for physical sputtering so that for CFC targets, only chemical sputtering remains as a source for the impurity in flux close to the strike-point areas [2]. Chemical sputtering can be described as a function of ion energy, ion flux and surface temperature [3], though uncertainties with respect to data interpretation and extrapolation to detached plasma conditions exist. Recent experiments in Asdex-Upgrade and DIII-D at low surface temperatures (T surface ≅ 350K) showed a reduction of the intrinsic hydrocarbon flux and the chemical sputtering yield under detached conditions in comparison to attached conditions in high density plasmas [4,5].…”

CH spectroscopy for carbon chemical erosion analysis in high density low temperature hydrogen plasma

“…CH spectroscopy relies on the correlation between CH radiation and methane particle fluxes, 6 the main reaction product formed upon chemical erosion of carbon. 7 The method is widely applied in fusion experiments and provides insight that is presently used to make predictions for ITER plasma wall issues. Also for ITER it would be an obvious diagnostic.…”

Dynamic Monte-Carlo modeling of hydrogen retention and chemical erosion from Tore Supra deposits

“…18 [17] and the divertor of ASDEX Upgrade [18] (All data are published in [16]). The solid line is a fit to the experimental data [16].…”